1. Technical Field
This disclosure relates to devices which convert analog input signals into digital output signals and particularly to systems which convert analog input signals into digital output signals using low resolution analog to digital converters.
2. Related Art
Analog to digital (A/D) conversion may be used in many applications including digital microphony. In digital microphony, signals with a wide dynamic range are transmitted while maximizing the signal-to-noise ratio (SNR). High performance analog to digital converters may be used for this purpose. However, high performance converters may be expensive and may consume a significant amount of power, making high performance converters undesirable for portable applications, such as radio microphones.
Gain staging may attempt to avoid these costs by splitting the analog input signal into two analog signal components and subjecting the two analog signal components to different levels of amplification. The two analog signal components may occur in different signal paths having different signal levels and may be independently subjected to independent A/D conversion. If a signal component subjected to a high amplification increases above a threshold, clipping may occur in an A/D converter. In this instance, a switchover to the lower level signal component or the corresponding signal path may occur. Due to its lower level, clipping may not occur in the corresponding A/D converter.
In gain staging two or more low-resolution converters may be used in place of one high-resolution converter without limiting or influencing the dynamic range that is available for transmission. The gain staging, however, is caused by switching between the two signal paths, which may require a precise matching of the digitized signal components to each other. The digitized signal components may need to be matched in both the amplitude and the phase. Time shifts as small as a nanosecond may cause unwanted interferences at the “junctions” at which one signal component is attached to the other signal component The effort expended by the complicated matching of the signal components is not related to the simplification of the actual A/D conversion.
Other systems that replace a high resolution A/D converter with multiple low resolution A/D converters may pass signal components through a nonlinear network. After passing through the nonlinear network the signal components are directed into two signal paths. One of the signal components is distorted such that it contains substantially no useful information from the input signal below a threshold signal level. The other signal component results from the addition of the input signal with a correct sign to the distorted signal component. A complementary distorted signal shape is produced. After performing an A/D conversion of the two signal components, the original input signal is reconstructed through the addition of the two digitized signal components. Since the distortion of the signal components may be accurately complementary, the resulting signal may be an undistorted digital output signal. The decrease in amplitude due to the subtraction of the distorted signal may prevent the corresponding A/D converter from reaching the clipping level. While these systems may avoid some of the problems of switching between the signal paths, there may be interferences in these systems, such as when the analog input signal has high signal and noise amplitudes.